1. Field of the Invention
The present invention relates to a bundle of long thin carbon structures. More specifically, it relates to a bundle of long thin carbon structures that can be used as an electronic element for various electronic devices.
2. Description of the Related Art
In recent years, so-called carbon nanotubes (CNTs) and other tubular carbon materials discovered among carbon fibers have been studied as electronic elements with the properties of electrically conductive and thermally conductive bodies for use in semiconductor integrated circuit devices including semiconductor devices, printed circuit boards and other various electronic devices {see for example Japanese Patent Application Laid-open No. 2005-022885 (claims)}.
There has been particular interest in CNTs as materials for forming semiconductor devices because of their excellent chemical stability and unique physical, electrical and other properties, and research continues into means of controlling their thickness and length, formation position, chirality and the like.
FIG. 11 shows one example of a wiring via structure using such CNTs (see for example Japanese Patent Application Laid-open No. 2002-329723 (claims) and Nihei et al., Japanese Journal of Applied Physics, 2005, Vol. 44, p. 1626). As shown in FIG. 11, such a via structure can be prepared, for example, by forming an underlayer 2 and a Cu wiring layer 3 on a substrate 1, then depositing a barrier layer 4 (Ta film or the like) on this Cu wiring layer 3 to prevent dispersion of Cu, and then forming an insulating layer 5 on top, then forming a via hole, depositing a catalytic metal support film 6 (a Ti film for example) and a catalytic metal film 7 of a material such as Co by sputtering or the like, then growing CNTs 8 by chemical vapor deposition (CVD) or the like using hydrocarbon gas (CH4, C2H2, etc.), and then forming upper wiring.
In the conventional CNT wiring, the contact between the CNT wiring extending from the via and the upper wiring generally has a structure in which a metal electrode is simply vapor deposited on the CNTs grown out of the via.
However, it has been shown that a via with such a structure does not make effective use of the good electrical properties of the CNTs themselves because high contact resistance occurs between the CNTs and the upper wiring.
One reason for this has to do with the uneven lengths of the individual CNTs. As a result, the ends of the CNTs are not aligned, making it difficult to form a uniform contact between all CNTs and the electrode metal. One method of solving these problems is to polish the ends flat, but although a superficial flatness can be achieved by reducing the CNTs through polishing until they are aligned with the via, this does not completely solve the problem of uneven length, and it has been found that this would not necessarily be a suitable method since it causes cracking and other physical damage to the CNTs themselves.
The same problem exists when CNTs are used as thermally conductive materials in heat removal bumps for example. That is, because the ends of the CNTs are not uniform or aligned, their good thermal conductivity may be greatly reduced when they are brought into contact with another material.